This invention relates generally to the art of depositing films onto substrates by vacuum sputtering, and, more specifically, to the deposition of electrically conducting films by a cylindrical magnetron type sputtering apparatus using two targets.
There are many applications where films are deposited onto substrates by sputtering techniques. Once such application is in the coating of large substrates, such as glass for building windows, vehicle windshields, and the like. Several thin film layers are stacked one on top of each other in order to control the reflection and/or transmission of various light wavelength bands. Each of these layers is formed by sputtering, according to a common commercial technique, in a vacuum chamber. In such applications, it is desirable to form the film with a carefully controlled thickness over the surface of the substrate. In most cases, it is desirable that the thickness be uniform over the entire substrate but, in other cases, some controlled variation in thickness across the substrate surface is desired.
Such a cylindrical magnetron type sputtering apparatus includes a target composed of an element to be sputtered, held adjacent the magnetic structure that defines an erosion zone on the surface of the target. That is, the magnetic structure confines and directs the ions of a plasma, formed adjacent to the target surface, at a high velocity against the target in its erosion zone in order to dislodge atoms of the element desired to be sputtered away. An electrical power supply is connected to the target as a cathode and to another surface within the vacuum chamber as an anode. Some proportion of free electrons within the target plasma generally travel around the defined erosion zone, sometimes called a "race track". However, some percentage of these electrons escape from the magnetic containment as they travel around the race track, and are then collected by the anode. It is known that the size and position of the anode can affect the profile of the deposition rate across a substrate, among other factors.
The target can be a static form, often with a planar surface. It is generally preferred, however, to form the target on an outside surface of a cylinder that is rotated about its elongated axis. The target surface is thus constantly being moved through the stationary magnetic field. The target surface is then more uniformly eroded and thus better utilized. Two sets of rotating magnetron assemblies are often positioned side by side within a single vacuum chamber.
It is a primary object of the present invention to provide a dual target magnetron, and technique for using such a system, which has a uniform rate of deposition across a substrate when moving past the targets.
It is another object of the present invention to provide an improved anode structure for a dual target magnetron.